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cksum(1)							      cksum(1)

NAME
       cksum - Displays the checksum and byte count of a file

SYNOPSIS
       cksum [file...]

STANDARDS
       Interfaces  documented on this reference page conform to industry stan‐
       dards as follows:

       cksum: XCU5.0

       Refer to the standards(5) reference page	 for  more  information	 about
       industry standards and associated tags.

OPTIONS
       None

OPERANDS
       The path name of a file to be checked.

	      If no file is specified, standard input is used.

DESCRIPTION
       The  cksum  command  reads the files specified by the file argument and
       calculates a 32-bit checksum Cyclic Redundancy Check (CRC) and the byte
       count for each file. If no files are specified, standard input is read.
       The checksum, number of bytes, and file name are	 written  to  standard
       output. If standard input is used, no path name is printed.

       The  cksum command can be used to compare a suspect file copied or com‐
       municated over noisy transmission lines against	an  exact  copy	 of  a
       trusted file. The comparison made by the cksum command may not be cryp‐
       tographically secure; however, it is unlikely that an accidentally dam‐
       aged file will produce the same checksum as the original file.

       [Tru64 UNIX]  The cksum command uses a different algorithm than the sum
       command to calculate the 32-bit checksum CRC.  The cksum command uses a
       CRC algorithm based on the Ethernet standard frame check.  In addition,
       the sum block count is an octet count in cksum.

       [Tru64 UNIX]  The IEEE Std 1003.2-1992 and  X/Open  CAE	specifications
       require a slightly different method of calculating checksum values.  To
       obtain these new standards, set the  environment	 variable  CMD_ENV  to
       xpg4 as follows: export CMD_ENV=xpg4

       [Tru64  UNIX]  To  maintain  compatibility  if the environment variable
       CMD_ENV is not set, the default action of the cksum command reports the
       traditional checksum values.

       The CRC checksum is obtained in the following way:

       The encoding is defined by the generating polynomial:

       G(x)  =	x^32  + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^8 +
       x^7 + x^5 + x^4 + x^2 + x + 1

       Mathematically, the CRC value corresponding to a given file is  defined
       by  the	following procedure: The n bits to be evaluated are considered
       to be the coefficients of a mod 2 polynomial M(x) of degree n-1.	 These
       n  bits are the bits from the file, with the most significant bit being
       the most significant bit of the first octet of the file	and  the  last
       bit being the least significant bit of the last octet, padded with zero
       bits (if necessary) to achieve an integral number of  octets,  followed
       by  one	or more octets representing the length of the file as a binary
       value, least significant octet first. The  smallest  number  of	octets
       capable	of  representing  this integer is used.	 M(x) is multiplied by
       x^32 (that is, shifted left 32 bits) and divided by G(x)	 using	mod  2
       division,  producing  a	remainder R(x) of degree less than or equal to
       31.  The coefficients of R(x) are considered to be a  32-bit  sequence.
       The bit sequence is complemented and the result is the CRC.

EXIT STATUS
       The  following  exit values are returned: All files were processed suc‐
       cessfully.  An error occurred.

EXAMPLES
       To display the checksum and the size, in bytes,	of  file1  and	file2,
       enter:  cksum  file1  file2  3995432187	     1390     file1 3266927833
       20912   file2

       This output shows that the checksum of the file1 file is 3995432187 and
       contains	 1390  bytes,  and  that  the  checksum	 of  the file2 file is
       3266927833 and contains 20912 bytes.

ENVIRONMENT VARIABLES
       The following environment variables  affect  the	 execution  of	cksum:
       [Tru64  UNIX]  If this variable is set to xpg4, the method of calculat‐
       ing checksum values specified by IEEE  Std  1003.2-1992	(POSIX.2)  and
       X/Open  CAE  specifications  is used.  Provides a default value for the
       internationalization variables that are unset or null. If LANG is unset
       or  null,  the corresponding value from the default locale is used.  If
       any of the internationalization variables contain an  invalid  setting,
       the  utility  behaves as if none of the variables had been defined.  If
       set to a non-empty string value, overrides the values of all the	 other
       internationalization  variables.	  Determines the locale for the inter‐
       pretation of sequences of bytes of text data as characters  (for	 exam‐
       ple,  single-byte  as  opposed  to  multibyte characters in arguments).
       Determines the locale for the format and contents  of  diagnostic  mes‐
       sages  written  to  standard error.  Determines the location of message
       catalogues for the processing of LC_MESSAGES.

SEE ALSO
       Commands:  sum(1), wc(1)

       Standards:  standards(5)

								      cksum(1)
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